cache.py 文件源码

def acquire(self):
        """
        Attempt to acquire the lock, returning a boolean that represents if the
        lock is held.
        """
        # NOTE: This isn't API compatible with the standard Python
        # ``Lock.acquire`` method signature. It may make sense to make these
        # compatible in the future, but that would also require changes to the
        # the constructor: https://docs.python.org/2/library/threading.html#lock-objects

        time_remaining = self.seconds_remaining
        if time_remaining:
            raise LockAlreadyHeld('Tried to acquire lock that is already held, %.3fs remaining: %r' % (time_remaining, self))

        self.__acquired_at = None

        delay = 0.01 + random.random() / 10
        for i in xrange(int(self.timeout // delay)):
            if i != 0:
                sleep(delay)

            attempt_started_at = time()
            if self.cache.add(self.lock_key, '', self.timeout):
                self.__acquired_at = attempt_started_at
                break

            if self.nowait:
                break

        return self.__acquired_at is not None